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Life of the Aquatic Moth: the mystery behind underwater cocoons

The aquatic moth is a fascinating benthic macroinvertebrate that goes through a complete metamorphosis, involving the complete four stages of the life cycle; the egg, larval, pupal, and the adult stage. Today we will explore what happens after the aquatic moth pupae leaves the safety and familiarity of the water. And how does the aquatic moth pupae transform into its adult form? To explore these questions, we’ll start at the very beginning-- when the aquatic moth eggs are first laid.

Female aquatic moths will deposit their eggs on rocks under the water surface during the night. Some pond-dwelling species may attach their eggs to the underside of leaves that are hanging over the surface of the water. These eggs will take 6 days to 2 weeks to hatch unless they are deposited in the fall time in which case they will overwinter as eggs.

In their larvae phase, they will go through up to 5-7 stages of development called instars. Their lifespan at this stage is heavily dependent on environmental conditions.

As fully developed larva, they will now transform into the pupal phase by creating a cocoon using leaves and silk in the water. The transformation to the adult phase usually takes one month’s time and when complete, the pupa will chew a tiny slit along the one side of the cocoon and begin to emerge.

After emerging from the cocoon as an adult, the aquatic moth will swim to the water’s edge and escape the water, seeking for shelter and a dry place to wait until its wings are dry. After the wings dry they are able to take flight.

The lifespan of the adult aquatic moth can range from one day to two months depending again on the environmental conditions. Aquatic moths will stay close to aquatic environments even while continuing the rest of their lives on terrestrial ecosystems. Overall the entire lifespan of an aquatic moth is about 1 year.

Fun Fact: Adult male aquatic moths live longer than females.

Fun Fact: Aquatic moths will differ from terrestrial moths in that they have filamentous gills along their body and may even have a portable case.

Fun Fact: In at least one species, the adult female moth is completely aquatic and never emerges from the water.

Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.

Carina is an Environmental Education Assistant with the Changing Currents Program at EcoSpark. She is passionate about aquatic ecosystems and educating young minds on the connections between land and water. She recently graduated with a degree in Environmental Studies from York University and a diploma in Ecosystem Management Technology from Sir Sandford’s Fleming College, School of Environmental and Natural Resource Sciences.